[nrf fromtree] net: possibility to set custom link layer address length

This commit adds a new Kconfig option NET_LINK_ADDR_CUSTOM_LENGTH
that allows to set custom link layer address length if your link layer
technology is not supported directly. If this option is set to a value
greater than 0, that value is used as link layer address length.

Signed-off-by: Jani Hirsimäki <[email protected]>
(cherry picked from commit 9800ff5)

Author: jhirsi

include/zephyr/net/net_linkaddr.h

@@ -30,7 +30,9 @@ extern "C" {
  */
 
 /** Maximum length of the link address */
-#if defined(CONFIG_NET_L2_PHY_IEEE802154) || defined(CONFIG_NET_L2_PPP)
+#if CONFIG_NET_LINK_ADDR_CUSTOM_LENGTH > 0
+#define NET_LINK_ADDR_MAX_LENGTH CONFIG_NET_LINK_ADDR_CUSTOM_LENGTH
+#elif defined(CONFIG_NET_L2_PHY_IEEE802154) || defined(CONFIG_NET_L2_PPP)
 #define NET_LINK_ADDR_MAX_LENGTH 8
 #else
 #define NET_LINK_ADDR_MAX_LENGTH 6

subsys/net/ip/Kconfig

@@ -767,6 +767,14 @@ config NET_HEADERS_ALWAYS_CONTIGUOUS
 	  NET_BUF_FIXED_DATA_SIZE enabled and NET_BUF_DATA_SIZE of 128 for
 	  instance.
 
+config NET_LINK_ADDR_CUSTOM_LENGTH
+	int "Size of custom link layer address length"
+	default 0
+	help
+	  This option allows to define custom link layer address length
+	  if your link layer technology is not supported directly.
+	  As a default, custom link layer address length is not used.
+
 # If we are running network tests found in tests/net, then the NET_TEST is
 # set and in that case we default to Dummy L2 layer as typically the tests
 # use that by default.